Count nouns refer to things perceived as units with well defined
borders. They can be pluralized (balls, trees) directly enumerated
(three balls, fourteen trees), accept the indefinite article "a" (if the
language has one: a ball, a tree). About such things one asks: "How
many . . .?". They are opposed to mass nouns, which refer to things
perceived as "stuff" or substance (rice, spaghetti, flour), which cannot
under normal circumstances be pluralized (*rices, *spaghettis, *flours)
or enumerated (*three rices, *fourteen spaghettis), and in English take
the indefinite article "some" (some rice, some spaghetti). About such
things one asks "How much . . .?" Mass nouns can behave grammatically
like count nouns if used with a "unitizer" (grain of rice, strands of
spaghetti, cups of flour).